12: LINQ to Entitie s Over view in C#.NET

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12: LINQ to Entitie s Over view
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end We will look at concrete examples when we review the code generated by the EF designer The metadata for an association is represented by the in the namespace
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Entity Framework Components EF is implemented in two separate layers, as shown in Figure 123 The EntityClient Data Provider layer is the lower layer that translates from EDM concepts into native SQL concepts The Object Services layer provides additional services such as entity classes, a LINQ implementation, and an for change tracking
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Connection (to EDM Model) Command (Entity SQL) DataReader (Entities as Data Records)
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ADONET V2 Data Provider (Command, Connection, DataReader)
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LINQ extension methods are implemented for LINQ are translated into Entity SQL and, in turn, queries against into native avors of SQL supported by an ADONET V2 Data Provider The concepts in the EntityClient layer closely resemble the ADONET V2
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concepts of Connection, Command, and DataReader However, they are enhanced by EDM constructs For example, the connection in the EntityClient layer contains not only the database connection information but also information about the EDM model les The EF Object Services layer is very similar to a typical Object Relational Mapping layer It knows how to translate queries, materialize objects, ensure identity, and track changes It also manages optimistic concurrency and transactions
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This section walks you through the steps for using the Entity Framework in Visual Studio 2008 SP1 We will use the graphical designer to generate a model from the Northwind sample database Then we will use the generated classes for a simple set of operations on objects created from Northwind data As described in 7, A Quick Tour of LINQ to SQL, be sure that you have set up a connection to the database In Visual Studio, select View, Server Explorer, Solution Explorer In the Server Explorer pane, shown in Figure 124, be sure that you can view the tables in your database Appendix A contains tips for connecting to a database Next we will outline the steps to generate an entity data model so that it can be used for CRUD operations
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Server Explorer showing the Northwind database
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12: LINQ to Entitie s Over view
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Entity Model Generation Create a new project in Visual Studio Here we will use a C# console application named NorthwindEF In Solution Explorer, right-click the NorthwindEF project and choose Add, as shown in Figure 125
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Add New Item for using EF
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In the Add New Item dialog, shown in Figure 126, select Data in the left pane and ADONET Entity Data Model in the right pane, and click Add Select ADONET Entity Data Model, and choose a suitable name, such as Northwindedmx Click Add to bring up the Entity Data Model Wizard, as shown in Figure 127 This wizard helps you set up the connection and create a model from a database Choose Generate from Database and click Next
Using the Entity Framework
The Add Entity data model
Entity Data Model Wizard step 1: Generate from the database
12: LINQ to Entitie s Over view
Select the mdf le or connection from the drop-down for the Northwind database, as shown in Figure 128 The Entity connection string shows the information used by the EntityClient Data Provider It has information about the three model les and the connection string for use by the next layer the relational data provider
Entity Data Model Wizard step 2: Select a connection
Click Next to go to the next step: selecting database objects that will be used to generate a model, as shown in Figure 129 Expand the Tables node, and check Customers and Orders, as shown in Figure 1210
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Entity Data Model Wizard step 3: Expand database objects for the model
Entity Data Model Wizard step 4: Select database objects for the model
12: LINQ to Entitie s Over view
Click Finish to generate the model The wizard generates the Northwindedmx le, which shows the two entities and the relationship between them (see Figure 1211) Each entity also shows the navigation properties that let you navigate to another entity For example, the Customers entity for navigating to Orders entities The lower has a property named pane shows the mapping information for the entity selected on the designer surface Note that unlike LINQ to SQL designer, because EF designer does not perform smart plural-singular changes, you may want to use the renaming feature in Visual Studio to create more palatable entity names, such as Customer and Order